This invention relates generally to a belt steering system and more particularly concerns a device to steer a belt to maintain proper belt tracking characteristics while at the same time eliminating or minimizing edge stress induced on the belt which causes belt failure.
In a typical electrophotographic printing process, a photoconductive member is charged to a substantially uniform potential so as to sensitize the surface thereof. The charged portion of the photoconductive member is exposed to a light image of an original document being reproduced. Exposure of the charged photoconductive member selectively dissipates the charges thereon in the irradiated areas. This records an electrostatic latent image on the photoconductive member corresponding to the informational areas contained within the original document. After the electrostatic latent image is recorded on the photoconductive member, the latent image is developed by bringing a developer material into contact therewith. Generally, the developer material comprises toner particles adhering triboelectrically to carrier granules. The toner particles are attracted from the carrier granules to the latent image forming a toner powder image on the photoconductive member. The toner powder image is then transferred from the photoconductive member to a copy sheet. The toner particles are heated to permanently affix the powder image to the copy sheet.
Many commercial applications of the above process employ a photoconductive member in the form of a belt which is supported about a predetermined path past a plurality of processing stations to ultimately form a reproduced image on copy paper. The location of the latent image recorded on the photoconductive belt must be precisely defined in order to have the various processing stations acting thereon optimize copy quality. To this end, it is critical that the lateral alignment of the photoconductive belt be controlled within prescribed tolerances. Only in this manner will a photoconductive belt move through a predetermined path so that the processing stations disposed thereabout will be located precisely relative to the latent image recorded thereon. Lateral movement of the photoconductive belt is particularly a problem in connection with color copiers where the precise tracking of the belt is mandatory for acceptable copy quality.
When considering control of the lateral movement of the belt, it is well known that if the belt were perfectly constructed and entrained about perfectly cylindrical rollers mounted and secured in an exactly parallel relationship with one another, there would be no lateral movement of the belt. In actual practice, however, this is not feasible. Due to the imperfections in the system""s geometry, the belt velocity vector is not normal to the roller axis of the rotation, and the belt will move laterally relative to a roller until reaching a kinematically stable position.
Typically, the belt edge position is monitored and a steering roll is tilted to cause the belt to track in a desired direction to keep the belt in the desired lateral position. The tilting of a roll with the tensioned belt thereon causes a sloping tension distribution across the width of the belt with the greatest tension at the edge of the belt. This tension produces a stress at the portion of the belt that is least able to bear the excess stress, the edge.
Accordingly, it is desirable to develop a belt steering system that uses a steering roll and other support and drive rolls, which reduces or minimizes the stress induced at the very edge of a belt.
The following disclosures may be relevant to various aspects of the present invention:
The relevant portions of the foregoing disclosures may be briefly summarized as follows:
U.S. Pat. No. 5,467,171 to Castelli et al. describes a web steering roll for supporting the web being adapted for rotational movement about a first axis and tilting movement about a second axis transverse to the first axis is used. A compact internal tilting mechanism utilizing a motor inside of the roll connected at one end to a first pin extending outwardly from one end of said steering roll, the first pin being positioned eccentrically of the rotary axis, and a second pin extending outwardly at the other end of the roll also positioned eccentrically of the rotary axis and connected to the motor through a connecting mechanism so that when said motor is actuated the second pin rotates in a direction opposed to that of the first pin.
U.S. Pat. No. 4,061,222 to Rushing discloses an apparatus for tracking an endless belt along an endless path by a tiltable belt steering roller whose position is continually adjusted so that the belt is maintained at a stable equilibrium position despite changes in the belt shape. The adjustment is determined by control circuitry which produces signals representative of lateral belt edge position, a desired belt edge position, and either a steering roller position or an instantaneous lateral belt deviation rate to produce a control signal which is applied to a gear motor to control the tilt angle of the steering belt roller. This apparatus utilizes the absolute control method.
U.S. Pat. No. 4,572,417 to Joseph et al. discloses an apparatus for controlling lateral, cross track alignment of a web moving along a path to minimize lateral deviation between successive discrete areas of the web. A steering roller supports the web for movement along the path and is rotatable about an axis perpendicular to a plane of the span of the web approaching the steering roller.
U.S. Pat. No. 4,170,175 to Conlon, Jr. discloses a system for tracking an endless belt which automatically compensates for creep of the belt. The belt is supported by four rollers. A first is a drive roller, a second and third are idler rollers, and a fourth roller is an idler roller with flared ends. The flared roller provides passive tracking without electronic or active feedback. One of the idler rollers is spring loaded such that when an edge of the belt creeps up on one of the flared ends of the fourth roller, that side of the spring loaded roller is caused to tilt due to increased belt stiffness on that side. This positions the belt laterally toward a central position.
U.S. Pat. No. 4,174,171 to Hamaker et al. disclose an apparatus for controlling the lateral alignment of a moving photoconductive belt. A resilient support constrains lateral movement of the belt causing a moment to be applied to a pivotably mounted steering post. As a result, the steering post pivots in a direction to restore the belt along a predetermined path. This apparatus is passive and provides no active electronic feedback.
U.S. Pat. No. 4,344,693 to Hamaker disclose an apparatus for controlling the lateral alignment of a moving photoconductive belt. Lateral movement of the belt causes a frictional force to be applied to the belt support. The frictional force tilts the belt support to restore the belt to the predetermined path of movement. This apparatus is passive and provides no active electronic feedback.
U.S. Pat. No. 4,961,089 to Jamzadeh discloses a method and apparatus for controlling lateral movement of a web along an endless path. The lateral position of the web is monitored and a determination is made by a control unit if the web is within predetermined limits such that a copying operation can be completed while the web is still properly tracking. If the web is not tracking properly, or if it is predicted that the web will track beyond its predetermined lateral limits within a copying operation, a correcting step is taken prior to the copying operation. The correcting step determines a tilt angle for a steering roller. Upon completion of the correcting step, the apparatus returns to a monitoring capacity and does not provide corrective measures until the web is beyond or is predicted to go beyond the predetermined limits during a subsequent copying operation. This insures that copying operations have proper registration and do not include corrective steps during the copying operation which might interfere with the registration. This apparatus uses an absolute scheme to determine corrective action.
U.S. Pat. No. 5,078,263 to Thompson et al. discloses an active steering method that introduces corrective skew through a small rotation about the xe2x80x9csoft-axisxe2x80x9d of one or more idler rolls. The skew is introduced by an external connection to a servomotor to alter the angle at which the web enters or leaves the roll to cause the web to walk along the roll.
In accordance with one aspect of the present invention, there is provided an apparatus for controlling a web moving along a predetermined path. The apparatus comprises an apparatus for controlling and driving a web moving along a predetermined path, comprising a web steering roll for supporting the web, said web steering roll being adapted for driven rotational movement about a first axis and tilting movement about a second axis transverse to the first axis, said web steering roll comprising a cylindrical member supported for rotational movement about its longitudinal axis wherein each end of said cylindrical member is radiused to provide a nonsharp contact point with the web, means for sensing movement of the web in a direction substantially normal to the predetermined path and generating a signal indicative thereof and means, responsive to the signal generated by said sensing and generating means, for tilting said steering roll about the second axis, to return the web to the predetermined path.
Pursuant to another aspect of the present invention, there is provided an electrophotographic printing machine of the type having an endless photoreceptor belt supported by a plurality of rolls and arranged to move in a predetermined path through a plurality of processing stations disposed therealong. The improvement includes a belt steering roll for supporting the belt, said belt steering roll being adapted for driven rotational movement about a first axis and tilting movement about a second axis transverse to the first axis, said belt steering roll comprising a cylindrical member supported for rotational movement about its longitudinal axis wherein each end of said cylindrical member is radiused to provide a nonsharp transition from contact, within the belt edges, means for sensing movement of the belt in a direction substantially normal to the predetermined path and generating a signal indicative thereof; and means, responsive to the signal generated by said sensing and generating means, for tilting said steering roll about the second axis, to return the belt to the predetermined path.